1. Field of the Invention
The present invention relates to processing mushrooms in general and in particular to a novel salt-free treatment liquid for impregnating mushrooms comprising a mixture of starch, gum, protein and water.
2. Description of Prior Art
Various methods have been used in the past to prepare mushrooms for canning. In one such prior known method the mushrooms are washed and peeled and then blanched in boiling water for a period of six to ten minutes. The blanching inactives the mushroom enzymes, coagulates the mushroom protein and expels the air therefrom due to shrinkage.
Disadvantages of this method are that the volume of the mushrooms is reduced, soluble aromas are reduced, mushroom albumin is reduced and the mushrooms undergo a significant weight loss. In addition, it has been found that there is a tendency for the mushrooms to turn grayish-brown during sterilization and blacken when they are exposed to air after the can in which they are stored is opened.
To reduce the above-described loss of weight, color, taste and texture of the mushrooms, various vacuum processes were developed in which the mushrooms are impregnated with treatment liquid comprising water and/or a variety of ingredients.
In one such prior known vacuum process the mushrooms are subjected to a vacuum and impregnated with a treatment liquid comprising a mixture of water or mushroom juice obtained from boiling mushrooms in water and a colloidal substance selected from the group consisting of egg white, casein, milk albumin (lactalbumin) and carrageenan.
In the prior known vacuum process described above, which is disclosed in U.S. Pat. No. 4,328,251, issued to Blanchaud et al, the colloidal substance in the treatment liquid, e.g. egg white, comprised between 10% to 25% by weight relative to the weight of the treatment liquid. The mushroom juice and/or water and the colloidal substance in the treatment liquid are thoroughly homogenized through slow agitation or by ultrasonics. After the mushrooms are placed in a vertical or inclined vacuum chamber, the chamber is evacuated to a pressure on the order of 50 to 60 mm Hg for a relatively long period of time on the order of 6 to 10 minutes to remove air and other gases present in the interstices of the mushrooms. At the end of the vacuum treatment, the treatment liquid is drawn into the vacuum chamber by the vacuum in the chamber to cover the mushrooms with the treatment liquid. After releasing the vacuum, the mushrooms are permitted to remain in the treatment liquid for a period of 5 to 10 minutes. Following the impregnation, the mushrooms are removed from the vacuum chamber, thoroughly washed in running water and blanched in boiling water for 6 to 10 minutes to coagulate the colloidal substance impregnated in the mushrooms.
In two earlier patents disclosing substantially the same vacuum process, U.S. Pat. No. 4,218,484 and U.S. Pat. No. 4,143,167, issued to the patentees of U.S. Pat. No. 4,328,251, the patentees also teach that the vacuum treatment period should be of a relatively long period of time on the order of 1 to 10 minutes, 2 minutes being usually sufficient, and that greater vacuums and longer vacuum treatment periods result in little, if any, improvement in the mushrooms. The patentees also teach that the optimum treatment liquid is characterized by a mixture of approximately equal parts of water and mushroom juice and a colloidal substance comprising 60 grams/liter of finely divided egg white or 280 to 420 grams/liter of liquid egg white. In an example of the results of using the process disclosed in the earlier patents, the patentees disclose that upon completion of the process, the weight of 1000 grams of mushrooms impregnated with the liquid treatment was reduced to 687 grams after the blanching treatment, i.e. a yield of about 69%.
In U.S. Pat. No. 4,735,813, issued to Spinoglio, there are disclosed other vacuum processes using treatment liquids for processing a variety of vegetables comprising mixtures of proteins and starches, such as rice starch, dispersed in 2% salt water. In this process, after brief thermal treatment, the mushrooms are rapidly cooled to gel the starches in a superficial part of the mushroom so as to form a seal. In still another vacuum process, in which actually appears to be a modification of the foregoing process, there is disclosed the use of ingredients for seasoning and/or enriching in nutritional elements, which may also include thickening agents such as starches and gums. This process, however, also appears to require the formation of a gel in the superficial part by rapid cooling so as to seal the mushroom or other vegetable being processed.
While providing an improvement over the prior known simple blanching process, the treatment liquids used in the above-described vacuum processes are found to have a number of disadvantages. For example, the use of egg white as a colloidal substance in the amounts indicated is very costly. The use of mushroom juice in the treatment liquid requires the additional step of boiling mushrooms to obtain the stock necessary to prepare the treatment liquid. The need for rapidly cooling the mushrooms to form a gel in a superficial part thereof is considered to be time consuming, costly and not particularly effective for maintaining a high yield. Furthermore, the use of salt in a treatment liquid significantly impairs impregnation and adversely affects yields.
The treatment of mushrooms with egg white in the amounts and in the manner disclosed produces a finished, canned product with a packing brine which contains visible amounts of feathery, coagulated albumin, similar in appearance to egg-drop soup. This feathery brine is perceived as undesirable by users of the canned product. The use of egg white alone, in addition to the high cost involved, produces mushrooms having a bland taste. The use of casein derived from dairy products or lactalbumin alone produces bad flavors. The use of water alone or starch and carrageenan (gum) alone produces a poor yield.